1. Field of the Invention
The present invention pertains to the field of control and audio manipulation of a digital audio signal by a user manipulable rotary control. The present invention is specifically applicable to manipulation of a digital audio signal by disc jockeys (DJs).
2. Description of the Prior Art
Scratch effects controllers for DJing has been come a popular replacement by DJs for conventional turntable and phonographic LP records for producing a scratch effect or to generally manipulate the speed and direction of music.
On a conventional turntable with a phonographic record, the DJ manipulates the rotating phonographic record by hand with a backward and forward motion to produce a scratch effect or to otherwise manipulate the speed and direction of the music playing on the phonographic record. Under normal use, i.e. when the user is not manipulating the phonographic record, a motor driven platter will rotate the record. When the user manipulates the record, the record will generally move independently of the rotating platter because there is slippage between the record and the platter surface.
Scratch effects controllers have been developed to simulate this user manipulation of a vinyl record on a phonographic turntable. Instead of a turntable, phonographic record, needle, and magnet cartridge, the scratch effect controller generally contains a user rotatable member. This user rotatable member can come in a variety of forms including a vinyl disc, metal or plastic platter, or a jog wheel. The surface is capable of freely rotating either clockwise or counter clockwise. There is generally some type of optical encoder and optical sensor operationally attached to the user rotatable member to detect speed, relative position, and direction of rotation. Some controllers try to more accurately simulate the functionality of a conventional phonographic turntable by having a rotatable platter under the user rotatable member. This platter is often driven by a motor in order to simulate the motion and feel of phonographic turntable platter. In this arrangement, the motion of the user rotatable member is detected by an optical encoder/sensor combination.
Some devices have incorporated an optical encoder pattern directly on the underside of the user rotatable member. For example, see U.S. Pat. No. 6,541,690 to Segers. Other devices mount the optical encoders below the surface of the rotating platter. For example, see U.S. Pat. No. 7,072,249 to Huang.
All of the above described controller devices have deficiencies in that highly accurate encoders are expensive, optical encoders are susceptible to dust, dirt and smoke, most optical encoder systems are only capable of detecting relative position, while detection of absolute position is desirable.